/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.messaging.handler.invocation;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.messaging.Message;
import org.springframework.util.Assert;
import org.springframework.util.concurrent.ListenableFuture;

/**
 * A HandlerMethodReturnValueHandler that wraps and delegates to others.
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public class HandlerMethodReturnValueHandlerComposite implements AsyncHandlerMethodReturnValueHandler {

    private static final Log logger = LogFactory.getLog(HandlerMethodReturnValueHandlerComposite.class);

    private final List<HandlerMethodReturnValueHandler> returnValueHandlers = new ArrayList<>();


    /**
     * Return a read-only list with the configured handlers.
     */
    public List<HandlerMethodReturnValueHandler> getReturnValueHandlers() {
        return Collections.unmodifiableList(this.returnValueHandlers);
    }

    /**
     * Clear the list of configured handlers.
     */
    public void clear() {
        this.returnValueHandlers.clear();
    }

    /**
     * Add the given {@link HandlerMethodReturnValueHandler}.
     */
    public HandlerMethodReturnValueHandlerComposite addHandler(HandlerMethodReturnValueHandler returnValueHandler) {
        this.returnValueHandlers.add(returnValueHandler);
        return this;
    }

    /**
     * Add the given {@link HandlerMethodReturnValueHandler}s.
     */
    public HandlerMethodReturnValueHandlerComposite addHandlers(
            @Nullable List<? extends HandlerMethodReturnValueHandler> handlers) {

        if (handlers != null) {
            for (HandlerMethodReturnValueHandler handler : handlers) {
                this.returnValueHandlers.add(handler);
            }
        }
        return this;
    }

    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        return getReturnValueHandler(returnType) != null;
    }

    @Nullable
    private HandlerMethodReturnValueHandler getReturnValueHandler(MethodParameter returnType) {
        for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) {
            if (handler.supportsReturnType(returnType)) {
                return handler;
            }
        }
        return null;
    }

    @Override
    public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType, Message<?> message)
            throws Exception {

        HandlerMethodReturnValueHandler handler = getReturnValueHandler(returnType);
        if (handler == null) {
            throw new IllegalStateException("No handler for return value type: " + returnType.getParameterType());
        }
        if (logger.isTraceEnabled()) {
            logger.trace("Processing return value with " + handler);
        }
        handler.handleReturnValue(returnValue, returnType, message);
    }

    @Override
    public boolean isAsyncReturnValue(Object returnValue, MethodParameter returnType) {
        HandlerMethodReturnValueHandler handler = getReturnValueHandler(returnType);
        return (handler instanceof AsyncHandlerMethodReturnValueHandler &&
                ((AsyncHandlerMethodReturnValueHandler) handler).isAsyncReturnValue(returnValue, returnType));
    }

    @Override
    @Nullable
    public ListenableFuture<?> toListenableFuture(Object returnValue, MethodParameter returnType) {
        HandlerMethodReturnValueHandler handler = getReturnValueHandler(returnType);
        Assert.state(handler instanceof AsyncHandlerMethodReturnValueHandler,
                "AsyncHandlerMethodReturnValueHandler required");
        return ((AsyncHandlerMethodReturnValueHandler) handler).toListenableFuture(returnValue, returnType);
    }

}
